This invention relates to a ride height control system for a tractor trailer suspension, and more particularly, for walking beam trailer suspensions.
Ride height control devices are used in tractor trailer suspensions to automatically control ride height of the tractor trailer suspension under predetermined conditions. For example, in response to load on the trailer, a height control valve can be used to inflate or deflate suspension air bags. Many trailer suspensions utilize tandem axle arrangements in which each axle is supported on a frame by a four bar linkage so that each axle moves independently of one another. In these configurations, the height control valve is supported on the frame and a rod is interconnected between one of the axles and the frame. The rod is pivotally connected to a lever on the height valve control that is rotated in response to vertical movement of the axle to open and close the height control valve. Proper valve operation requires the lever to be rotated approximately ±10° in either direction. This rotation requires approximately 2 inches of suspension travel, which is easily attainable in a four bar linkage tandem axle arrangement.
Walking beam suspension configurations are desirable in tandem trailer axle arrangements because of their increased stability and reduced tendency to dock-walk. Walking beam suspensions eliminate two upper links on each side of the four bar linkage configurations and replace them with a beam pivotally connecting each side of the axles. Incorporation of a height control valve into such a configuration is problematic because the height control valve must attach at a mid-point of the walking beam to best average the suspension travel of front and rear axles in the tandem trailer axle arrangement. Unfortunately, there is very little travel at the mid-point and the height control valves currently available are not sensitive enough to operate desirably under the limited vertical travel of a walking beam configuration.